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Security LED Blinker

What it does  - Makes the OEM Security Indicator LED in the instrument cluster blink on and off whenever the ignition is turned off, simulating an active security system.

Application - Only works on clusters from 2006 to 2009.  Earlier years do not have the Security LED in the cluster.

There are dozens of ways to do this but I think this is the easiest and least expensive.

     
PARTS:  (supply your own or I have a bare-bones parts kit available here). 
NOTE - You cannot use a 12-volt blinking LED for this project!
 

Special 3-volt blinking LED - Digikey part# 67-1499 ($1 ea)
Resistor - 100k ohms, 1/4 watt, 5% tolerance
Connector - 1/4" female quick-connect
Misc wire, tape, heat-shrink

  Locating the Security LED wire:

Behind the driver's side kick panel* is a 2-wire gray connector taped to the wire harness just above the hood release handle.  The black/yellow wire (black with a yellow stripe along the length) is the wire that goes to the security LED.

* For help on how to remove the kick panel see the installation instructions for my Yellow Jacket product, available on this page


 
   
Wiring:

Follow the wiring diagram below to connect the resistor to the ANODE side of the LED.  You can either solder the wires or twist them tightly together and cover with electrical tape or heat-shrink tubing.

You will then have to attach a short length of wire to the free end of the resistor.  The other end of this wire splices into the black/yellow wire in the security LED connector.

Attach a 1/4" female quick-connect terminal to another piece of wire, and then connect the opposite end of this wire to the LED CATHODE.  Make sure you insulate all exposed wires with tape or heat-shrink tubing.

The wire with the quick-connect terminal plugs into the ignition power terminal in the under-dash fuse box.  See photo on right to identify the correct terminal.

 

  Identify Ignition Terminal on Fuse Box:

Looking up under the driver's side dash you will see the fuse box.  There are 3 sockets with 1/4" male quick-connect terminals, you want the one

     

 
   
Parts Kit order here

Contains the blinking LED, 100k resistor, and quick-connect crimp terminal to plug into the fuse box.

You must supply your own wire, tape, etc to make the connections.

NOTE - You cannot use a 12-volt blinking LED for this project; it will not work.  I tried 2 different 12-volt LEDs and neither one works because there is not enough power available from the security LED circuit.  The LED in the kit is a special blinking LED that operates on 3 volts.

 
     
How it works:

The security LED in the cluster is operated by a transistor driver circuit that activates by a ground.  The black/yellow wire is connected to +12v through a resistor and the transistor is connected so it "sees" the voltage on that wire.  Normally the voltage is +12 and the transistor is OFF, but if you ground the black/yellow wire the transistor turns ON and lights the LED.

The LED will light any time the black/yellow wire is grounded and you can test this if you want (won't hurt anything).  Unlike most other lamps and indicators in the cluster, the security LED does get power from the "activation wire" (black/yellow).  The current to operate the LED comes from inside the cluster.  The black/yellow is just a trigger and requires very little current to operate, as little as .01 milliamps compared to the 10 or 20 milliamps that the LED uses.

On a car with the OEM security system, the micro-processor in the alarm module would pulse the black/yellow wire when the system was armed, alternately connecting it to ground or leaving it "open", thus causing the LED to blink.  In our application we are using the blinking LED to provide the ground pulse.  This blinking LED has an electronic circuit inside with a timer that pulses the LED on and off.  When the LED lights it has very low resistance, effectively connecting the black/yellow wire to ground and activating the security LED.

The resistor is needed because the security LED circuit is so sensitive that even the tiny bit of current used by the timer circuit in the blinking LED is enough to trigger the cluster LED.  By adding the resistor we reduce the current to a level where the "background" current of the blinking LED is not enough to trigger the cluster circuit, but when the LED blinks ON the increased current is enough to provide a ground to the cluster and the security LED lights.

If you know a little bit about electronics you might wonder how this works if we are connecting the black/yellow wire to ignition power (through the blinking LED)?  In other words, if it takes a ground to activate the cluster LED why connect it to +12?  When the ignition is ON it is true that the blinking LED and therefore black/yellow wire is connected to +12 volts, but when the ignition is off it is actually connected to ground through the various circuits (cluster, ECM, etc) that are tied to the ignition circuit.

Let's say the ignition circuit draws 3 amps when the ignition is turned on (a realistic figure).  Using ohms law, that tells us that the ignition circuit has a resistance of 4 ohms (12v divided by 3 amps = 4 ohms).  One side of that 4-ohm load is connected to ground all the time, and the other side is connected to the ignition key and the IGN terminal in the fuse box.  When the ignition key is switched ON, +12v is sent to the cluster, ECM, and the IGN terminal.  But when the key is OFF, the IGN terminal in the fuse box is connected to ground through the cluster and ECM, which we just determined has a resistance of 4 ohms.  For our sensitive LED circuit, a 4-ohm connection to ground is just as good as a direct connection to ground because it needs so little current to operate.

In this way, we effectively ground the blinking LED when the ignition is turned off.  Since the anode (+) side of the blinker is connected to +12v through the security LED circuit in the cluster, the blinker LED has power, causing it to blink and in turn make the security LED blink.